1. Field of the Invention
This invention relates to triple plenum air conditioning apparatus and more particularly to a triple-inlet, fan-powered, mixing box for use in single or multizone heating, ventilating, and air conditioning system.
2. Brief Description of the Prior Art
Triple plenum air conditioning apparatus which mix return air with hot or cold air are known in the art. The triple plenum systems were designed to reduce the energy consumption present in earlier systems. In earlier air conditioning systems for alternate heating and cooling, the heated air was mixed with the cooled air to provide a desired air temperature. This method was very wasteful of energy and generally unsatisfactory.
The most common triple plenum systems used in multizone systems comprise a central air handling unit wherein the central fan forces the air out at least two plenums at a time into the zone ducts. One plenum contains a heating device for providing warm or hot air and another contains a refrigerant evaporator coil or other device for providing cool or cold air and the third plenum simply neutral or return air. A return air duct, which may be an open return air space above the rooms in the building being heated or cooled, provides a plenum of ambient or neutral temperature air which is mixed with hot or cold air at the central air handling unit for disbursement through zone ducts.
A thermostat in the space controls an appropriate air flow damping system in the outlet ducts of the source in such a way that either heated air or cooled air or a mixture of one or the other with ambient air is delivered to the space. In order to conserve energy, it is necessary that air supplied to the space never be a mixture of heated air and cooled air. To this end, the duct for ambient air, generally referred to as bypass or return air, is usually interposed between the duct for heated air and the duct for cooled air and a damping system is required which will permit all heated air, a mixture of heated air with bypass air, all bypass air, a mixture of bypass air and cooled air, or all cooled air to be supplied to such space.
There are several patents which disclose triple plenum air conditioning apparatus for mixing hot or cold air with return air.
Wells, U.S. Pat. No. 3,847,210 discloses a rack and pinion damper sequencer for mixing bypass air with hot or cold air.
Perkins, U.S. Pat. No. 3,994,335 discloses a multizone air conditioning system which mixes recirculated air with hot or cold air. The system includes a single return air means for conducting the return air from the plurality of zones and a single shaft which operates a set of dampers to mix the return air with hot or cold air.
Timmerman, U.S. Pat. No. 4,164,976 discloses a damper assembly having interlocking members for interlocking adjacent damper assembly units together and adapted to be affixed to an air handling unit at an installation site. The damper assembly mixes ambient air with hot or cold air.
Ratner, U.S. Pat. No. 4,312,381 discloses an air flow damping system wherein a pair of spaced shafts each carrying a pair of planar damper blades are provided for mixing bypass air with hot or cold air. The hot air duct and the cold air duct each contain one damper blade and the bypass duct contains a first and second blade at right angles to each other. A control means is provided for maintaining both the first and second bypass blades in their fully open position and for rotating each shaft independently while maintaining the other stationary, to reciprocate one bypass blade between its fully open position and its fully closed position while reciprocating one of the hot air damper blade and cold air damper blade between its fully open and its fully closed position.
Gressett, U.S. Pat. No. 3,376,916 discloses a zone air conditioning apparatus utilizing a control or mixing box located between warm air and cold air inlet ducts and having a common outlet duct leading into a discharge which includes a fan on the downstream section. A circular baffle plate is disposed in the T-shaped section which serves to join the inlet ducts in coaxial relation. The baffle plate travels axially so as to traverse the opening of the common outlet duct to allow passage of warm air, cold air, or a mixture thereof to the zone being served.
Crombie et al, U.S. Pat. No. 3,911,953 discloses a triple plenum mixing damper having three planar blades in which the bypass air blade is fixed to a shaft and the other two are connected to the shaft by lost motion or overrunning spring couplings. The bypass blade is in the open position at the mid-point of shaft and the other blades are disposed at 45 degree angles relative thereto. In a first extreme position, the bypass blade extends 45 degrees across the bypass passage closing it off, the warm air blade extends parallel to the warm air passage opening it, and the cool air blade extends 45 degrees across the cool air passage closing it off. In a second extreme position, the bypass blade extends 45 degrees across the bypass passage closing it off, the warm air blade extends 45 degrees across the warm air passage closing it off, and the cold air blade extends parallel to the cold air passage opening it. In a third middle position, the bypass blade is parallel to the bypass passage opening it, and the warm air blade and cold air blade each extend 45 degrees across the warm air passage and the cold air passage, respectively, closing them off.
Marshall et al, U.S. Pat. No. 3,368,652 discloses a dual duct air distribution system adapted for seasonal change-over installation. Air flow is regulated by two different valves which operate in response to different actuating pneumatic pressures caused by a significant change in the pneumatic supply pressure which is provided within the building.
The prior art in general, and these patents in particular, do not disclose an air conditioning system including an automatically controlled triple inlet mixing box having a cold air inlet, a hot air inlet, a return air inlet, and a fan for inducting and disbursing the air mixed therein. Thermostatic motors regulate the rotation of first and second dampers having a configuration which controls opening or closing of the hot air inlet, the return air inlet, and the cold air inlet in a manner whereby the air mixture may be regulated from cold to neutral to hot. The cold air and the hot air are never mixed directly. The induction fan draws in the air from the open or partially open inlet openings to mix the same and discharge the mixture to the room. Several fan-powered mixing boxes may be incorporated into a multizone system with each zone regulated by a thermostat to mix the return air with hot or cold air to supply the desired zone temperature.
In a dual inlet embodiment of the fan-powered mixing box, the return air duct is connected to the hot air duct outside the mixing box and a portion of the hot air duct serves as the inlet for both hot air and return air. Dampers are positioned within the return air duct and the hot air duct. Inside the mixing chamber, the open ends of the hot air duct and cold air duct are positioned to be opened and closed by a single damper controlling both the hot air inlet and cold air inlet without any direct mixture of the cold air and the hot air at any time.